This invention relates generally to fireplace heaters and particularly relates to an improved forced-air fireplace heat exchanger capable of being positioned entirely within the fireplace.
A fireplace heat exchanger is a device placed in a fireplace for the purpose of extracting heat therefrom during combustion and providing heated air to adjacent areas. The extent to which such systems are capable of distributing heat depends primarily upon the rate at which air is circulated through the fireplace and the efficiency of heat transfer to the transported air in the fireplace. The prior art discloses various approaches for enhancing the heat transfer function such as extending the path of the moving air through the fireplace by means of extensive duct systems. One such approach is described in U.S. Pat. No. 3,190,282 to Bauer which makes use of an L-shaped structure having a horizontal portion which is placed on the floor of the fireplace and a vertical section which is positioned adjacent the fireplace's rear wall. Cold air is provided through an aperture to the vertical section which contains a duct system in which the air is circulated and heated. The heated air is then provided to the horizontal section from which it is forced out by means of convention into the adjacent area.
Another approach to a circulating air fireplace heat exchanger is disclosed in U.S. Pat. No. 4,096,849 to Moncrieff-Yeates wherein is described a fireplace unit having an inlet duct at the bottom of the fireplace, a vertical duct at the rear of the fireplace and an outlet duct near the top of the fireplace which is positioned over the area of combustion. The various ducts are angled with respect to the horizontal such that the heated air is always moving in an upward direction, thus providing for a self-circulating system which takes advantage of the rising effect of heated air. More recent attempts to further increase the heat extracted from a fireplace have made use of a source of forced air which is circulated through the fireplace thus providing for an increased volume of heated air. One such approach is described in U.S. Pat. No. 4,008,706 to Buanno in which air is circulated by means of a blower which projects the moving air along a baffle-deflected path through a housing which is positioned on the floor of the fireplace. The hot air exits the housing by means of an outlet positioned at the front of the housing for delivery to the area immediately adjacent to the fireplace. Another forced-air heating fireplace grate is disclosed in U.S. Pat. No. 4,010,729 to Egli wherein air is also forced into an inlet duct by means of a blower. An exhaust duct is coupled to the inlet duct by means of cross ducts through which the air flows while being heated by combustible materials resting primarily on the cross ducts. In these two patents the blower is positioned outside of the fireplace proper which is characteristic of prior art forced-air fireplace heat extraction systems.
It is desirable to position the heat extraction system entirely within the fireplace, not only to enhance aesthetic appeal, but also to reduce noise levels in the adjoining room produced by blower operation. Placing the entire heat extraction system in the fireplace subjects the blower mechanism and associated circuitry to extreme environmental conditions. This is particularly true where the heat extractor is utilized with a radiating type of firescreen which is typically equipped with glass doors. Heat buildup in the fireplace due to the positioning of the firescreen is substantially increased and, if the air flow through the heat extractor is interrupted, will likely destroy or substantially damage the blower and associated components.